Satellite communication systems typically have employed large aperture antennas and high power transmitters for establishing an uplink to the satellite. Recently, however, very small aperture antenna ground terminals, referred to as remote ground terminals, have been developed for data transmission at low rates. In such systems, the remote ground terminals are utilized for communicating via a satellite for a remote location to a central hub station. The central hub station communicates with multiple remote ground terminals, and has a significantly larger antenna, as well as a significantly larger power output capability than any of the remote ground terminals.
Very small aperture terminal (VSAT) remote terminals can be used to communicate data, voice and video, to or from a remote site to a central hub. Typically, the VSAT remote terminals have a small aperture directional antenna for receiving from or transmitting signals to a satellite, and an outdoor unit (ODU) mounted near the antenna for transmitting a modulated carrier generated by an indoor unit (ZDU). The ZDU demodulates incoming signals received from the ODU and also operates as an interface between a user's communication equipment and the ODU.
The outdoor unit functions in part as an interface between the indoor unit and the antenna. As such, it contains a transmitter chain for transmitting the modulated carrier signal and a receiver chain for coupling signals received via the antenna to the indoor unit. The outdoor unit further comprises a coupling apparatus, for example, a duplexer, which allows the transmitter chain and the receiver chain to be coupled to a single antenna.
Other coupling apparatus heretofore utilized contained various combinations of individual components, including multiple filters and transducers, coupled together as required to perform the necessary task of separating the signals to be transmitted from the received signals. Such separate components often require additional transitions and transformers in order to couple the outdoor unit with the antenna via a feedhorn. Such additional transitions and transformers operate to reduce the transmission capabilities of the outdoor unit by increasing insertion losses and other related factors. Further, the separate components were often located inside the outdoor unit and therefore were not readily field replaceable or readily upgraded once installed.
Accordingly, as the viability of the remote ground terminal concept increases as the cost for providing a remote ground terminal at the remote location decreases, it is necessary to decrease the cost of all components of the remote ground terminal as much as possible. As such, there exists a need for a coupling apparatus which is a single integrated unit which does not require a plurality of individual components or additional transitions and transformers to be utilized to interface the coupling apparatus with either the outdoor unit or the antenna. Further, the coupling apparatus should be readily removable from the outdoor unit so as allow, for example, the transmitter chain to be upgraded so as to provide an increase in transmission capabilities.